Light emitting diode circuits for general lighting

ABSTRACT

Improved circuits minimize, or eliminate, energy losses in LED lighting. Diodes and a capacitor reduce or eliminate blinking and create smooth and continuous infinitely variable dimming. The components supply power to each LED during the half of the AC cycle where it would normally be turned off. Added diodes allow an added capacitor to charge during the half cycle that the original diode is turned on, but does not allow the other half cycle to discharge the added capacitor. When the added capacitor is charged enough to turn on the original diode, it stays on throughout the AC cycle. Zener diodes protect the LEDs from voltage surge&#39;s/spikes by shunting current around LEDs when the voltage exceeds the Zener diode&#39;s breakdown voltage. A microprocessor controller with MOSFETs provides an ultra efficient embodiment with near zero power dissipation.

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/150,256, filed Apr. 25, 2008, which claims priority to provisionalpatent application Ser. No. 60/926,450, filed Apr. 27, 2007. The entirecontent of each application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The field of the invention pertains to electrical circuits for all lightemitting diodes and, in particular, for “white” or substantially all ofthe visual spectrum light emitting diodes.

LEDs are semiconductor devices that produce light when a current issupplied to them. “White” light emitting diodes (LEDs) are LEDs thatemit a full visual spectrum of light. Such LEDs took a considerablenumber of years to be developed and considerably more years to bebrought to mass production. In particular, only recently have white LEDswith lumen outputs sufficient for general lighting and thereforereplacement of incandescent or fluorescent lighting become available.White LEDs offer a very real reduction in energy cost in comparison withincandescent and fluorescent lights but also operate with a much lowertemperature rise.

Unfortunately, because white LEDs operate at a few volts and generallighting operates at 110 volts AC RMS or 220 volts AC RMS, eitherstrings of white LEDs in series or extensive and complicated passive(and sometimes active) electric circuit elements are employed to avoidthe application of over voltages to the white LEDs. Blinking from powertransient can be a problem. Another problem is that conventional (TRIAC)operated dimmers require the light to be turned on and then turned backdown to a lesser brightness. What was needed was a smooth and continuousvariable dimming of LEDs.

SUMMARY OF THE INVENTION

The invention comprises improved electric circuits that are highlyefficient and minimize, if not substantially eliminate energy losses inthe supply of energy to and control of white LEDs. LED can be prototypepower line LED can be OPTEK OVSPW7CRB with custom heat sink rated at 350mA continuous.

Addition of two diodes and two capacitors arranged into a circuit(FIG. 1) increases efficiency and can reduce or eliminate LED blinking.These components are designed into the circuit to supply power to eachLED during the half of the AC cycle where it would normally be turnedoff. A first added diode allows a first added capacitor to charge duringthe half cycle that the original diode is turned on, but does not allowthe other half cycle to discharge the added capacitor. When the addedcapacitor is charged enough to turn on the original diode, it stays onthroughout the AC cycle. The same relationship exists between the secondadded diode, the second added capacitor and the second original diode.

The larger the added capacitor, the less variation there is in LEDbrightness, but the longer it takes for the LED to turn on initially.Filter capacitor in the circuit when simulated must be pretty large(4000 uF) and 160 mS is needed to turn on. Both LEDs stay on all thetime but vary in brightness. Larger capacitors reduce flicker fartherbut take longer to turn on. Voltage on one of the filter capacitorsincreases with each AC cycle until the voltage reaches the operatingvoltage of the LED.

N channel and P channel Low Loss MOS FETs are used for the circuit (FIG.8) to replace a small resistor in series with the Anode to Cathodeconnected LEDs. The purpose of the MOS FET's is to reduce the powerdissipated in the resistor. Some form of current limiting is necessaryduring the switch activation which if not done at the Zero Crossing ofthe applied AC Waveform, will cause huge current spikes in the LEDscausing then to open up (catastrophic failure). Using a resistor inseries with the LEDs will work, but will cause power to be wasted andcause the resistor to get hot. In the circuit, the power is applied tothe capacitor when the power switch is turned on. Initially, the MOSFETs are turned off, and only leakage current flows through the LEDs (afew uA or less). When power is applied to the circuit, the rectifierpasses the current to the Time Delay circuit if the voltage is such thatthe rectifier is forward biased. The Time Delay circuit will after sometime turn on the MOS FET's so that current can flow through theCAPACITOR/LED circuit. The Time Delay is such that the transient of theswitch closing is not seen, and the NMOS FETs are turned on in a gradualfashion.

The circuit also employs two Zener diodes connected in series with theircathodes tied together. With this configuration, the max Voltage drop isequal to the zener voltage plus the forward drop of one Zener diode. Thetwo Zener diodes are then connected in parallel with the Anode toCathode LED package so that if one LED opens up, the entire string doesnot go out (Christmas Tree Light Syndrome). The voltage drop across theseries Zener diodes is chosen to be slightly greater than the voltageacross the Back to Back LEDs. The Zener diodes protect the LEDs fromvoltage surges/spikes by shunting current around LEDs when the voltageexceeds the Zener diode's breakdown voltage.

1. This new Light Emitting Diode (LED) Dimmer is totally different fromconventional TRIAC operated dimmers. This new dimmer is very energyefficient and also will work at all dimmer settings of the incoming ACline voltage. This makes it possible to operate at light levels that arejust visible, and the diodes not have the annoying sudden “lights On”when turning the control from OFF to some ON level. This dimmer willinstead turn the LEDs on very gradually.

2. In a block diagram of the new LED dimmer circuit (FIG. 17), the 120VAC connects directly to a Capacitor that supplies power to threeblocks. The first block is the LOW VOLTAGE POWER SUPPLY that generateslow voltage DC for use by the Micro Processor based MOS FET Controller.The second and third blocks are voltage dividers that divide thevoltages by using two resistors so that the voltage going into the A/DConverter is within the operating range of the A/D. The two voltagesare: the Capacitor input voltage (Line Voltage), and the second is theCapacitor output voltage.

3. The fourth block (discussed below) is the Back to Back LEDs. Thereason that the LEDs are connected Anode to Cathode (Back to Back) is sothe Capacitor can have a conduction path for both polarities of theincoming AC power. The Capacitor supplies all the current for the LEDs,and yet dissipates next to zero power. The power of the Capacitor wouldbe classified in the “Dissipation Factor” which is less than 0.1%typical.

4. The Back to Back LEDs are connected to the parallel connected MOSFETs, one being an “N” channel and the other being a “P” channel. Thisis done so that both the negative side and the positive voltages of theincoming Line Voltage can be switched. The MOS FETs have a very low “ON”resistance making the Drain/Source voltage drop very low. Less than 100mV is the typical ON voltage drop that calculates in to a 0.029 W PeakPower loss. This is an exceeding low number, and makes it so that thevast majority of the Power Dissipation is in the LEDs themselves.

5. The MICRO PROCESSOR BASED MOS FET CONTROLLER (FIG. 17) reads theinstantaneous line voltage from its on-board A/D. The sequence ofoperation is: A. The Dimmer is turned from OFF to some ON value. TheDimmer can be a potentiometer or two push button switches. B. The MicroProcessor senses that the LEDs want to turn on. C. The Micro Processorlooks at the LINE VOLTAGE DIVIDER and also the CAPACITOR VOLTAGEDIVIDER. If the voltages match within some small value that is hardcoded, the Micro Processor turns on one of the MOS FETs. Initially, theCAP voltage would be Zero volts, so the MOS FET would be turned on atZero volts. D. Depending on the setting of the Dimmer Control, the MicroProcessor turns off the N Channel MOSFET, and stores the Line Voltageand the Capacitor Voltage in RAM. (As an example +40V is used). D. Whenthe Live voltage has gone up to the +160v and is coming back down, theMicro Processor turns ON the N Channel MOS FET at +40V. Doing this makesit so that only a very small (or no) current transient will occur in theCapacitor/LED circuit. F. At the Zero Voltage Crossing point, the MicroProcessor turns off the N channel MOS FET, and turns on the P ChannelMOS FET. At −40V, the Micro Processor turns OFF the P Channel MicroProcessor MOS FET and waits for it to go to −160 V and then back to−40V. At −40V, the P Channel turns back on and stays on until ZeroCross.

6. G. Go to 5 D, and repeat.

7. Section 5 makes it so the Capacitor does not have Step Functionchanges in voltage which will cause very large current transients in theLEDs.

For a more complete understanding of the present invention, reference ismade to the following detailed description when read with in conjunctionwith the accompanying drawings wherein like reference characters referto like elements throughout the several views, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a circuit to control LED blinking;

FIG. 2 illustrates LED current vs. time for the circuit of FIG. 1;

FIG. 3 illustrates voltage on one of the filter capacitors for thecircuit of FIG. 1;

FIG. 4 illustrates voltage vs. time for capacitor C2 in the circuit ofFIG. 1;

FIG. 5 illustrates voltage vs. time for capacitor C3 in the circuit ofFIG. 1;

FIG. 6 illustrates voltage vs. time for Capacitor C1 in the circuit ofFIG. 1;

FIG. 7 illustrates the addition of multiple diodes for added LEDs in thecircuit of FIG. 1;

FIG. 8 illustrates a circuit with transistors (MOS FET) to reduce powerconsumption in the circuit;

FIG. 9 illustrates a block diagram of the circuit in FIG. 8;

FIG. 10 illustrates a circuit with Zener diodes to protect circuitagainst LED failure or voltage spikes;

FIG. 11 illustrates a block diagram of a more sophisticated Zenerprotected circuit;

FIGS. 12 a, 12 b, 12 c and 12 d illustrate typical multi-meter readingsfor the circuit in FIG. 10;

FIG. 13 illustrates the step in Zener voltage in the circuit of FIG. 10;

FIG. 14 illustrates the step in LED string voltage in the circuit ofFIG. 10;

FIG. 15 a illustrates the back of an 8 LED light array for generalillumination;

FIG. 15 b illustrates the Zener circuit for the light array of FIG. 15a;

FIG. 16 a illustrates a simple circuit for a three-stage LED lightdimmer circuit;

FIG. 16 b illustrates a truth table for the LED light dimmer of FIG. 16a;

FIG. 17 illustrates a block diagram for a substantially infinitelyvariable LED light dimmer;

FIG. 18 illustrates a simulation circuit of invention of FIG. 17;

FIG. 18 a illustrates a graph of capacitor voltage for the light dimmerof FIG. 17;

FIG. 18 b illustrates a graph of capacitor plus LED voltage for thelight dimmer of FIG. 17;

FIG. 18 c illustrates a graph of capacitor plus LED current for thelight dimmer of FIG. 17; and

FIG. 19 illustrates a graph of the on and off portions of the sinusoidalinput for the dimmer of FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illustrated in FIG. 1 is simulated LED power supply circuit 10 tocontrol blinking having typical AC voltage with capacitor 12 selected toprovide the necessary current for the LEDs 14, 16. Addition of twodiodes 20 and 26 with capacitors 22, 24 to circuit 10 as shown reducesor eliminates LED blinking. Capacitors 22 and 24 are filter capacitors.Diodes 20 and 26 and capacitors 22 and 24 are added to supply power toeach LED during the half of the AC cycle where each LED would normallybe turned off. Diode 20 allows capacitor 22 to charge during the halfcycle that diode 16 is turned on, but does not allow the other halfcycle to discharge capacitor 22. When capacitor 22 is charged enough toturn on diode, 16 it stays on throughout the AC cycle. The samerelationship exists between diode 26, capacitor 24 and diode 14.

The larger the capacitors 22 and 24, the less variation there is in LEDbrightness, but the longer it takes for the LED to turn on initially.Filter capacitor in the circuit is large as (4000 uF) and 160 mS isneeded to turn on.

Analysis results of circuit 10 of FIG. 1 are depicted in FIGS. 2-7.Current displays differently through each LED (FIG. 2). Voltage on oneof the filter capacitors for circuit 10 is shown in FIG. 3. Voltage vs.time for capacitor 22 in the circuit 10 is shown in FIG. 4. FIG. 5illustrates voltage vs. time for capacitor 24 in circuit 10 of FIG. 1.Voltage vs. time for capacitor 12 in circuit 10 is depicted in FIG. 6.Illustrated in FIG. 7 is addition of multiple diodes for added LED's incircuit 10 of FIG. 1.

Now turning to FIG. 8, thereshown is circuit 10 employing transistors(MOS FET) to reduce power consumption in circuit 10. Circuit 10 of FIG.8 is better shown in block diagram in FIG. 9.

Circuit 10 using Zener diodes 28, 30 to protect against LED failure orvoltage spikes is illustrated in FIG. 10, while FIG. 11 shows a moresophisticated Zener protected analog circuit 10 in block diagram.Elimination of power transient is shown in an analog circuit FIG. 11 andin a digital circuit FIG. 18. Typical multi-meter readings for points inthe circuit of FIG. 10 are depicted in FIGS. 12 a, b, 12 c and 12 d.Step in Zener voltage in circuit 10 of FIG. 10; is shown in FIG. 13while FIG. 14 illustrates step in LED string voltage in circuit 10 ofFIG. 10. Back of 8 LED light array for general illumination isillustrated in FIG. 15 a. Zener circuit for light array of FIG. 15 a isshown in FIG. 15 b.

Simple circuit for a three-stage LED light dimmer circuit is shown inFIG. 16 a. Truth table for LED light dimmer circuit of FIG. 16 a isdepicted in FIG. 16 b.

Substantially infinitely variable LED light dimmer is depicted in blockdiagram in FIG. 17. Circuit of FIG. 18 replicates block diagram of FIG.17 for simulation purpose. Results of circuit of FIG. 18 are shown ingraphs FIGS. 18 a, 18 b, 18 c and 19 with power ON at zero cross, OFF atvoltage X, ON at voltage X, OFF at voltage Y and ON at voltage Y.

Capacitor voltage for the light dimmer of FIG. 17 is depicted in graphFIG. 18 a. Capacitor plus LED voltage for the light dimmer of FIG. 17 isshown in graph FIG. 18 b. Capacitor plus LED current for the lightdimmer of FIG. 17 is depicted in FIG. 18 c.

On and off portions of the sinusoidal input for the dimmer of FIG. 17are shown in the graph of FIG. 19 using MOS FETs.

Having described the invention, many modifications thereto will becomeapparent to those skilled in the art to which it pertains withoutdeviation from the spirit of the invention as defined in the appendedclaims.

1.-16. (canceled)
 17. A circuit that minimizes blinking in alight-emitting diode (LED) circuit adapted for connection to analternating current (AC) line voltage, comprising: a light-emittingcircuit including a first LED connected in series with a first diode, asecond LED connected in series with a second diode, and wherein thefirst LED and diode are connected in parallel with the second LED anddiode such that current flows through the first LED and diode during onehalf-cycle of the AC line voltage and current flows through the secondLED and diode during the other half-cycle of the AC line voltage; thelight-emitting circuit further including a first filter capacitorconnected in parallel across the first LED and a second filter capacitorconnected in parallel across the second LED; and a resistor andcapacitor connected in series with each other and in series with thelight-emitting circuit.
 18. The circuit of claim 17, wherein the filtercapacitors are electrolytic.
 19. The circuit of claim 17, wherein eachfilter capacitor is thousands of microfarads.